The application for setting up an enhanced uplink in the low chip TD-SCDMA system is approved by 3GPP (3rd Generation Partnership Project) in March 2006. The enhanced uplink is generally called HSUPA (High Speed Uplink Packet Access), which aims for improving the efficiency of the uplink through advanced technique to effectively support web browse, video, multimedia information and other IP-based services.
Although the TD-SCDMA of 3GPP has no complete technical report until now, the basic technical framework has been developed and it is basically consistent with that of the TD-CDMA system. For the basic technical framework, which can refer to proposal and conference report in 3GPP conference held in Shanghai in May, and the related technical framework of the present invention is described as follows.
A transmission channel E-DCH (Enhanced-uplink Dedicated transmission Channel) for carrying the uplink data is added in HSUPA, and the TTI (Transmission Time Interval) of the E-DCH is 5 ms.
The new added physical channels are:
E-AGCH (E-DCH absolute grant channel), which is a control channel used for Node B to transmit the grant information;
E-PUCH (enhanced physical uplink channel), which is a traffic channel used for the UE (User Equipment) to carry E-DCH encoding combination and aided scheduling related information;
E-RUCCH (HSUPA random access uplink control channel), which is a physical control channel used to transmit the aided scheduling related information when UE has not been granted, and E-RUCCH uses the random access physical channel resource;
E-HICH (E-DCH HARQ indication channel), which is a control channel used for Node B to carry HARQ indication information.
According to scheduling method, HSUPA service is divided into scheduling service and non-scheduling service, where the resource of the non-scheduling service is assigned to UE by SRNC (Service Radio Network Controller), and the assignment method is the same as that of the dedicated channel in the prior art; The scheduling service is based on the scheduling of Node B which sends absolute grant information including power grant information and physical channel grant information to the UE through the E-AGCH. The grant information is not sent to the UE in each TTI (Transmit Time Interval), and it is totally up to the scheduling function entity of the Node B to determine whether to send the grant information and when to send it according to the network condition and the parameter QoS (Quality of Service) of the UE. The UE intercepts one group of E-AGCHs, and the UE reads the grant information once the information is decoded successfully and sends the data through the granted E-PUCH after a time period prescribed by the protocol.
Another key technology used by the enhanced uplink is parallel stop-wait HARQ technology which is used to implement the rapid retransmission of the wrong packet. The entity processing the HARQ function is located in the MAC-es/e (enhanced media access control sub-entity/enhanced media access control entity) at the UE side and in the MAC-e (enhanced media access control entity) in Node B, and one HARQ entity supports several examples of the stop-wait HARQ protocol, and each example is called as a HARQ process. Although the number of parallel processes in one HARQ entity has not been determined yet, it is not less than 4, and one HARQ process relates to a physical layer buffer which is used to cache the data to facilitate the retransmission at the sender side and to combine softly and decode at the receiver side. The HARQ entity at the UE side is used to save and retransmit the MAC-e PDU (protocol data unit); The HARQ entity at the Node B side is used to generate ACK or NACK indication for a single MAC-e PDU and send the indication to the UE through the E-HICH.
In the TD-SCDMA enhanced uplink technology, a group of logical channels belonging to one UE with the same QoS are mapped to the same MAC-d (dedicated media access control) flow, and one UE can support 16 logical channels, 8 MAC-d flows at most, and the higher layer admits several MAC-d flows multiplexed into a MAC-e PDU at most and configures MAC-d flow multiplexing list for each MAC-d flow, the QoS of MAC-d flows in the list is close to that of the MAC-d flow. When assembling the MAC-e PDU, the data are multiplexed according to the priorities of the logical channels, meanwhile, the multiplexing list of the MAC-d flow in which the logical channel with the highest priority is located configured by the higher layer should be considered. The higher layer configures a HARQ Profile (service attribute) including the maximum number of retransmissions (which also can be “the maximum number of transmissions’, and “the maximum number of retransmissions” is “the maximum number of transmissions” minus one) and power offset for each MAC-d flow to show the QoS attribute of each MAC-d flow.
The maximum number of retransmissions in the HARQ Profile of one MAC-e PDU is generated according to the following rules:
The maximum number of retransmissions is the maximum one of the maximum numbers of retransmissions of all MAC-d flows multiplexed into this MAC-e PDU;
The maximum number of retransmissions shows the delay and the residual bit rate requirements of the MAC-e PDU. When a new transmission begins, the HARQ entity provides a HARQ process with the MAC-e PDU and its HARQ profile, wherein the maximum number of retransmissions is used for the HARQ process to give up retransmission when the number of PDU retransmissions surpass the maximum number of retransmissions.
FIG. 1 shows the MAC-es/e at the UE side, wherein the E-TFC (enhanced transmission format collection) selection entity selects the length of the transmission block for the new data according to the grant information; The multiplexing and TSN (Transmission Sequence Number) setting entity is responsible for putting several MAC-d PDUs from one logical channel to the MAC-es (enhanced media access control sub-entity) PDU, and multiplexing one or several MAC-es PDUs to one MAC-e PDU and generating the HARQ Profile according to the selection result of the E-TFC selection entity; The scheduling access entity is responsible for obtaining and regulating the signaling information related to the scheduling; The HARQ entity is responsible for processing the HARQ protocol, including saving and retransmitting the MAC-e PDU.
FIG. 2 shows the flow of data transmission, in which after the grant is received, retransmission is primarily considered, a suitable retransmission packet is selected to notify the corresponding HARQ process to retransmit, and the retransmission processing of the HARQ process is as follows: the information such as retransmission sequence number and power offset is provided to the physical layer for retransmission, and the value of the retransmission counter is automatically added by 1; If the value of the counter surpasses the maximum number of retransmissions of this MAC-e PDU, the packet is discarded, the HARQ process is cleared, and the packet will not be retransmitted. If there is no retransmission packet or the granted resource is not suitable for the present retransmission packet after a grant is received, the E-TFC selection entity is notified to select the transmission format; The multiplexing and TSN setting entity assembles the MAC-e PDU and generates the HARQ profile; The HARQ entity selects a free process to transmit new data, and the process of HARQ process is as follows: the information such as transmission format, retransmission sequence number, process number and power offset is provided to the physical layer and the retransmission counter is cleared to zero.
The Node B sets up a MAC-e for each UE using the enhanced uplink, and one scheduler controls the scheduling of the UE, generates ACK and NACK indication for single MAC-e, and de-multiplexes the MAC-e PDU as MAC-es PDUs; The SRNC creates one MAC-es for each UE using the enhanced uplink, which is used to reorder and de-multiplex the MAC-es PDUs, wherein the reordering mechanism is similar to that in the present HSDPA.
The scheduling service in the TD-SCDMA enhanced uplink applies synchronous confirmation and asynchronous retransmission HARQ mechanism. Taking the scheduling service as an example, the timing relationship is shown as FIG. 3: after the UE receives the E-AGCH grant information, it sends data through E-PUCH after the timing T1 and then receives HARQ indication through the E-PUCH from Node B after the timing T2, if the received information is NACK, the UE will not retransmit the data until it receives the absolute grant and the waiting time is T3; if the received information is ACK, the UE will discard the data block, clear the related HARQ process, and wait for the next grant to transmit new data. Wherein, T1 and T2 have definite timing relationship, and T3 is variable, which depends on the scheduling of Node B.
The HARQ asynchronous retransmission mechanism applied today can not guarantee the retransmission time of the MAC-e PDU, because the delay requirement of QoS in the radio bearer can not be guaranteed only depending on the configuration of the number of retransmissions, and in the transmission mechanism of the upper layer RLC (radio link control) using the confirmation mode, the MAC layer of the UE is not allowed to perpetually wait for retransmission resources.
In addition, when the MAC-es at the network side performs reordering, timer mechanism and window mechanism are always applied to avoid reordering buffer congestion and sequence number confusion. The timer mechanism is used to avoid waiting for the packet with low sequence number too long in non-ordering transmission; the window mechanism is used to avoid the sequence number confusion, and since the sequence number space of the packet is limited, the sequence numbers of the new and old packets may be the same in the retransmission mechanism system, which will result in the sequence number confusion at the receiver side. Nowadays, the 3GPP organization definitely points out that this portion is not standardized and it is SRNC internal processing mechanism, which, however, needs cooperation from the UE side to avoid unnecessary retransmission. For example, without the cooperation from the UE side, there is possibility that the reordering timer at the network side is timed out but the number of transmissions at the UE side has not surpassed the maximum number of retransmissions, thus the retransmitted data from the UE side will not be processed at the network side, which will result in unnecessary retransmission.